Perilous summoning is *too* perilous. It appears to clone summoned monsters that are placed on squares iterated later in the loop than the original, as well as the original monsters. The result: I was surrounded by something like 50 scrawny cats and 20 hobbit revelers, starting with one of each.
Edit: overland travel should not pick handfuls of berries or other things that have side effects to eat automatically. There's food in the pack too!